The present invention relates to a hybrid vehicle having an engine and a motor, or, in particular, to a hybrid vehicle in which the fuel consumption can be improved by 5 controlling the operating point of the engine and the battery charging rate according to a target.
One system intended to reduce engine fuel consumption is a hybrid vehicle utilizing the driving force of the motor. Various types of such systems have been proposed, and they include the series type and the parallel type. For example, JP-A-7-135701 discloses a system in which two motors and one planetary gear are used so that the engine driving force is input to the planetary gear, and the motor is controlled in order to drive the vehicle by the driving force obtained from the output shaft of the planetary gear. Part of the energy of the engine is derived from a generator (which is one of the motors) generates power while the motor coupled to the output shaft of the generator delivers a driving force as an assistance. Thus, the engine is always driven efficiently in a high torque area while at the same time providing the shift function.
A method of controlling the driving torque of a hybrid vehicle is described in JP-A-8-207601, in which the torque of the generator is calculated and the torque of the motor on the output shaft is corrected by the calculated torque of the generator. According to this method, the vehicle driving torque is not greatly affected by variations in the engine output, and, therefore, the drivability can be improved.
In order to suppress the change in the charging condition of the battery connected to the generator or the motor, on the other hand, JP-A-10-243503 discloses a method in which the motor torque command or the target engine speed is corrected in accordance with the current value of the battery. This method makes if possible to maintain the normal condition of the battery, and, therefore, the deterioration of the battery can be prevented. Also, the battery charging rate can be controlled as scheduled.
Of all the methods described above, the method of correcting the output of the motor according to the estimated torque value can control the vehicle drive torque as intended, and, therefore, can improve the drivability. Nevertheless, the change in motor output may cause an unexpected charge and discharge of the battery, often leading to the deviation from the optimum schedule for charging the battery, resulting in a deteriorated fuel consumption rate.
According to the method of correcting the motor output or the target engine speed in accordance with the battery current or the like, on the other hand, battery deterioration can be prevented and an optimum schedule can be followed. However, the required driving output cannot be produced, which often adversely affects the drivability.
In any of the methods described above, the engine operating point, if deviated from the target, is not corrected, thereby posing the problem that the engine deviates from the optimum operating point and the fuel consumption rate deteriorates.
An object of the present invention is to provide a hybrid vehicle in which the efficiency and the fuel consumption can be improved by controlling the engine operating point and the battery charging rate as intended, without adversely affecting the drivability.
In order to achieve the aforementioned object, according to the invention, a hybrid vehicle is provided comprising an engine for generating the energy for driving the vehicle, a transmission for transmitting the driving force to the wheels by changing the rotational speed of the engine, at least a motor for changing the wheel driving force, a battery for supplying power to the motor, and a drive control unit for calculating and outputting an operation command value for the engine and the motor. This is based on the drive information including the accelerator angle, wherein the drive control unit includes an engine output correcting mechanism for correcting the operation command value for the engine, based on the difference between the engine operation command value and the torque generated by the engine, in order to maintain an optimum engine operating point.
The optimum operating point is defined as a point on or near a curve associated with the best fuel consumption rate of the engine, including the efficiency of the transmission and the motor.
According to another aspect of the invention, a hybrid vehicle is provided comprising an engine for generating the energy for driving the vehicle, a transmission for transmitting the driving force to the wheels by changing the rotational speed of the engine, at least a motor for changing the wheel driving force, a battery for supplying power to the motor, means for determining the target engine torque, means for calculating the torque generated by the engine, and means for correcting the engine output, based on the difference between the target engine torque value and the engine torque value calculated by the engine torque calculation means.
According to still another aspect of the invention, a hybrid vehicle is provided comprising an engine for generating the energy for driving the vehicle, a transmission for transmitting the driving force to the wheels by changing the rotational speed of the engine, at least a motor for changing the wheel driving force, a battery for supplying power to the motor, means for determining a target engine output value instead of the engine torque, means for calculating the output of the engine, and means for correcting the engine output, based on the difference between the target engine output value and the calculated engine output value.
According to yet another aspect of the invention, a hybrid vehicle is provided comprising an engine for generating the energy for driving the vehicle, a transmission for transmitting the driving force to the wheels by changing the rotational speed of the engine, at least a motor for changing the wheel driving force, a battery for supplying power to the motor, a battery management unit for determining a target current value of the battery, means for detecting the battery current, and means for correcting the engine output based on the difference between a target battery current and a detected battery current value, wherein the battery management unit produces a schedule for the battery charging rate based on the navigation information, and determines the target battery current value based on the difference between the detected value of the battery charging rate and the scheduled battery charging rate.
The engine output correcting means can correct the output by controlling the degree of the throttle opening degree or correcting the target engine output value.
According to this invention, an optimum engine operating point can be maintained while producing the target vehicle driving torque, and also the battery charging rate can be kept as scheduled for an improved fuel consumption 25 rate.